It is difficult, without spilling, to pour oil from a usual can, bottle or similar container into the filler inlet for an automotive engine oil reservoir, unless a funnel is used. That is because the container usually has a short neck (or no neck), the container usually is nearly completely full, and the vicinity of the filler inlet may be obstructed by other structures. In time of need, a funnel may not be available. This leads to undesirable spills and to an undue reluctance to give proper attention to adding oil to the engine.
Although engine oil is given as a ready example, there are other situations in which a comparable problem arises due to the difficulty of pouring a liquid, without spillage, from an open neck of a container, without the aid of a funnel.